Hi John:
First off, the rechargeables I'm using are the Lennmar 2400 mh NiMH. My point here is I would not assume all are created equal, and different brands may vary on shelf-life and use-life.
That said, in my AFD3 body:
1) I notice no significant loss of life if the camera is left sitting unused, batteries left in the camera, even over several weeks of sporadic use.
2) I noted a definite improvement in total life after the second charge cycle, like about double. The first charge got me maybe 250 clicks before death, or about the same as one fresh battery in my P45+ back.
3) From the second charge on, I would say that life has doubled, or close to it. I now get about 1-1/2 to 2 changes of batteries in my P45+ back per cycle of AA charge, or about 400-500 frames total.
4) Needless to say, I carry the 6 rechareables in the camera, 6 spare rechargeables in the bag, and at least a dozen emergency alkalines nearby...
5) Note that the Lenmar speed charger I bought came with 4 batteries and charges 4 batteries in about 30 minutes, so it takes about an hour to recharge a set of 6 using the single charger. I then bought an extra pack of 10 cells, so I have 14 total cells. I am planning on buying a second charger so I can recharge a whole set of 6 cells in a half hour, and then I'd end up with 3 full sets of cells or 18 batteries total.
Hope that helps,